Sleep stages

Drowsy states

1. Slow lateral eye movement (SEM)

• less than 0.5Hz
• the first obvious electrographic signs of drowsiness    

 2. Small fast irregular eye movements

Stage 1 sleep

1. Disappearance of alpha rhythm, appearance of 4‐7Hz slow
2. Presence of SEM
3. Reduction of m. artifacts
4. V waves
5. POSTs
6. Frontocentral theta activity 

Stage 2 sleep

• Sleep spindle :> 0.5 sec
• K- complex:

Stage 3 sleep

• High-amplitude slow delta activity :> 50%

Rapid eye movement sleep 

• >50%  of  30  sec  epoch  low  voltage voltage  EEG  activity activity  with  prominent prominent theta activity preceded by rapid eye movements
•  rapid eyeball movement
• Reduced muscle activity
• Resemble the pattern of stage 1 sleep except  no  V  waves,  sawtooth shaped  wave  on  central central  &  frontal regions, alpha waves 1‐2Hz less than alpha rhythm.